Genetic analysis of the population structure of socially organized oystercatchers (Haematopus ostralegus) using microsatellites

On the island of Schiermonnikoog (The Netherlands), the breeding population of oystercatchers can be divided into two groups: 'residents' and 'leapfrogs', based on their distinct social characteristics and limited probabilities of status change between breeding seasons. In order to investigate whether this social organization has caused local genetic differentiation, leapfrogs and residents were compared at eight polymorphic microsatellite loci. No significant genetic subdivision between residents and leapfrogs was observed (theta = 0.0000; 95% confidence interval (CI), -0.0027-0.0033), indicating that the oystercatcher population on the island of Schiermonnikoog has to be considered as one panmictic unit. Investigation of three additional locations in the northern part of The Netherlands did not reveal significant genetic population subdivision either (theta = -0.0005; 95% CI, -0.0045-0.0037), despite the fact that adult osytercatchers show extreme fidelity to their breeding localities. These results indicate panmixis and considerable levels of gene flow within the northern part of The Netherlands. Thus, the results from genetical analyses do not seem to be in agreement with observational data on the dispersal behaviour of breeding individuals. It is argued that the lack of population structure, locally on Schiermonnikoog as well as across larger geographical distances, is to be attributed to high levels of gene flow through dispersal of juvenile birds.     

Cerastoderma glaucum 5S ribosomal DNA: characterization of the repeat unit, divergence with respect to Cerastoderma edule, and PCR-RFLPs for the identification of both cockles.

The 5S rDNA repeat unit of the cockle Cerastoderma glaucum from the Mediterranean and Baltic coasts was PCR amplified and sequenced. The length of the units was 539-568 bp, of which 120 bp were assigned to the 5S rRNA gene and 419-448 bp to the spacer region, and the G/C content was 46%-49%, 54%, and 44%-47%, respectively. Two types of units (A and B), differing in the spacer, were distinguished based on the percentage of differences and clustering in phylogenetic trees. A PCR assay with specific primers for each unit type indicated that the occurrence of both units is not restricted to the sequenced individuals. The 5S rDNA units of C. glaucum were compared with new and previously reported sequences of Cerastoderma edule. The degree of variation observed in C. edule was lower than that in C. glaucum and evidence for the existence of units A and B in C. edule was not found. The two cockles have the same coding region but displayed numerous fixed differences in the spacer region and group separately in the phylogenetic trees. Digestion of the 5S rDNA PCR product with the restriction enzymes HaeIII and EcoRV revealed two RFLPs useful for cockle identification.     

Predation of cockles (Cerastoderma edule) by the whelk (Buccinum undatum) under laboratory conditions

The feeding rate and behaviour of whelks (Buccinum undatum)offered cockles (Cerastoderma edule) in laboratory experimentswere examined. When presented with cockles in a range of sizes(10–40 mm), 14 B. undatum (34.6–88.3 mm),held individually in aquaria, consumed a wide size range ofcockles. Small whelks (<40 mm) consumed cockles (<23 mm),whereas large whelks, (>60 mm) ate a greater numberof larger cockles (>30 mm) and a wider size range ofcockles (12–40 mm) than smaller whelks. The majority(90%) of the shells of the predated cockles were undamaged andthe few (<10%) that were damaged showed only slight abrasionsto the anterior and posterior shell margin. Filmed observationsof B. undatum feeding on C. edule showed a method of attackthat has not previously been reported and involved the use ofthe whelk's foot to asphyxiate the cockle or to pull the shellvalves apart. No filmed evidence was found for the previouslyreported shell ‘wedging’ technique for prising openthe closed shell valves of C. edule, although 10% of the shellsof consumed cockles in feeding experiments had damaged shellmargins. (Received 4 April 2007; accepted 30 June 2007)     

A silver spoon for a golden future: long-term effects of natal origin on fitness prospects of oystercatchers (Haematopus ostralegus)

1. Long-term effects of conditions during early development on fitness are important for life history evolution and population ecology. Using multistrata mark-recapture models on 20 years of data, we quantified the relation between rearing conditions and lifetime fitness in a long-lived shorebird, the oystercatcher (Haematopus ostralegus). We addressed specifically the relative contribution of short- and long-term effects of rearing conditions to overall fitness consequences. 2. Rearing conditions were defined by differences in natal habitat quality, in which there is a clear dichotomy in our study population. In the first year of life, fledglings from high-quality natal origin had a 1.3 times higher juvenile survival. Later in life (age 3-11), individuals of high-quality natal origin had a 1.6 times higher adult prebreeder survival. The most striking effect of natal habitat quality was that birds that were reared on high-quality territories had a higher probability of settling in high-quality habitat (44% vs. 6%). Lifetime reproductive success of individuals born in high-quality habitat was 2.2 times higher than that of individuals born in low-quality habitat. This difference increased further when fitness was calculated over several generations, due to a correlation between the quality of rearing conditions of parents and their offspring. 3. Long-term effects of early conditions contributed more to overall fitness differences as short-term consequences, contrary to common conceptions on this issue. 4. This study illustrates that investigating only short-term effects of early conditions can lead to the large underestimation of fitness consequences. We discuss how long-term consequences of early conditions may affect settlement decisions and source-sink population interactions.     

The palearctic oystercatcher Haematopus ostralegus, a natural definitive host for Gymnophalloides seoi

In order to verify the role of migrating birds as natural definitive hosts for Gymnophalloides seoi (Gymnophallidae), Palearctic oystercatchers, Haematopus ostralegus, were caught from several western coastal areas in the Republic of Korea and examined for intestinal flukes. Five (71.4%) of 7 oystercatchers were infected with 302-1,660 (mean 892) adult G. seoi. In intestinal sections of the host, worms were found in the intervillous space of the mucosal layer. We conclude that the oystercatcher is a natural definitive host for G. seoi.     

The pair bond and divorce among Oystercatchers Haematopus ostralegus on Skokholm Island, Wales

Mate changes of Oystercatchers were followed over a 15-year period. In 8.0% of instances, the pair split up between breeding seasons even when both members bred the second season. The likelihood of divorce was highest for birds aged five years, the modal age of first breeding. After divorce birds did not select an older or younger mate when re-pairing. Low hatching success increased the chances of divorce. Divorce was not followed by significant changes in clutch-size, laying date or nesting success (although females tended to be more successful).     

The cranial and cervical osteology of the european oystercatcher Haematopus ostralegus L.

The cranial and cervical osteology of the European oystercatcher, Haematopus ostralegus L. is completely described from both whole skeletons and spirit specimens. Contrary to previous reports, the postorbital ligament shows variability in bifurcation and attachment, with the posterior branch, where present, attaching either to the suprameatic process or the zygomatic process. In addition, the quadrate ligament, which had been described as originating from the suprameatic process, appears instead to attach to the zygomatic process in some specimens. The caudal mandibular fenestra, earlier considered absent in oystercatchers, is present in all specimens examined. The cranium is additionally distinguished by a number of features which may be unique to oystercatchers. A fourth, previously unrecorded, division of the maxillopalatine strut is present, while the palatine process of the premaxilla is reduced to a thickening along the edge of the premaxillary process of the palatine. The distinctiveness of the oystercatcher cranium is particularly evident in the area of the quadratomandibular articulation, which possesses features potentially important for stabilizing the joint. A deep retroarticular notch is present, guiding a large medial jugomandibular ligament along the posterior margin of the articulation. A lateral mandibular tuberosity, which is received dorsally by an emargination of the jugal arch and quadrate, may act as an osteological brace, preventing posterior shifting of the closed mandible. The 15 cervical vertebrae are divided on the basis of structural criteria into three sections.     

A proliferative disorder of possible hemic origin in the common cockle,Cerastoderma edule

A study is described concerning the infestation of a laboratory-reared Daphnia magna culture by the fungus Aphanomyces daphniae. The origin of this fungus is Lake Huron, Michigan, the water from which is used in the laboratory to culture daphnids and maintain fishes for toxicological testing. Infestations originate from the Lake during the autumnal and vernal homothermal periods. The fungus is apparently maintained in the laboratory in conjunction with the fishes. Onset of fungal infestations in zooplankton culture apparently is initiated by three types of stress: rising temperatures, declining dissolved oxygen values, and poor nutrition. These infections have been eliminated by separating the daphnid culturing facility from the fish facility, substituting an algal diet for a synthetic one, sterilizing all water, air, and glassware connected with zooplankton culture, and maintaining the daphnids in a constant temperature room with controlled dissolved oxygen levels in the culturing vessels.     

Individual and age differences in the feeding ecology of Oystercatchers Haematopus ostralegus wintering on the Exe Estuary, Devon

The habitats and foods used by a sample of marked individuals and by the whole population of Oystercatchers Haematopus ostralegus wintering on the Exe estuary, South Devon, are described. In the spring and early summer, only a few hundred immatures were present. Two thousand adults and several hundred juveniles arrived in late summer from the breeding grounds and remained until the following spring. The majority of the birds were then adults. At low water, most adults fed on the mussel Mytilus edulis beds and ate mussels. Most individuals specialised on this prey and ate little else. Some adults fed on mud-flats and sandflats within the estuary and along the coast, and specialised on a mixture of Nereis diversicolor and Scrobicularia plana or on Cerastoderma edule or Littorina spp. Though some juveniles ate mussels from the time they arrived, most did not. In winter, they took Scrobicularia on mudflats, earthworms Lumbricidae and leatherjackets Tipulidae larvae in fields and Spisula and mussels along the coast. At other times of year they mainly ate Nereis. However, as they grew older, more birds began to specialise on mussels, especially in their second, third and fourth summers when the adults were away. At high water, most birds roosted at the mouth of the estuary or along the coast. However, several hundred fed in the fields in winter with more doing so late in the winter on warm days on Neap tides when less time was available for feeding on the estuary in daylight. Birds feeding on Nereis and Scrobicularia at low water were most often seen in the fields, irrespective of age. Birds feeding on Mytilus and Littorina occurred there rarely, but no bird eating Cerastoderma was seen there. The findings are discussed in relation to age differences in feeding skills and ability to compete successfully with other birds.     

Modelling the population consequences of age- and sex-related differences in winter mortality in the oystercatcher, Haematopus ostralegus

A modelling approach is used to explore the effect of age and sex differences in oystercatcher ( Haematopus ostralegus ) winter mortality on population size, population structure and the population response to habitat loss or change. Increasing the mortality of first and second year birds reduced population size, but had very little effect on the proportion of the population that were adults. Increasing female mortality reduced population size and resulted in a male-biased population. A sex bias amongst birds of breeding age meant that there were fewer potential breeding pairs for a given population size, reducing the size of the breeding population and the breeding output. Increasing the mortality of one sex relative to the other reduced population size, even when mean adult mortality rates remained unchanged. Increasing the strength of density-dependent mortality in young birds caused a greater reduction in population size as habitat was lost. Increasing the strength of female density-dependent mortality had the same effect, even though male density-dependent mortality had been correspondingly reduced. Increasing density-independent or density-dependent winter mortality in one sex relative to another also exaggerated the disproportional effect of winter habitat loss on separate breeding subpopulations using the same overwintering area. These results suggest that any study of population dynamics should be aware of both age and sex differences in mortality. Conservationists should be particularly aware of any age or sex differences in diet or habitat use that may result in a differential response to environmental change.     

Influence of disseminated neoplasia, trematode infections and gametogenesis on surfacing and mortality in the cockle Cerastoderma edule

Cerastoderma edule is a widely distributed bivalve mollusc, commercially exploited throughout Europe and is also an important food source for birds and crustaceans. Recently, mass surfacing and mortalities of cockles have been observed and reported at sites in Ireland and elsewhere, particularly in the summer months. One such site is Flaxfort Strand, Courtmacsherry Bay, County Cork, Ireland, an important feeding area used by many seabirds during the summer months. For the past few years large numbers of surfaced cockles have been observed at the site in a moribund condition. Samples of cockles from this area were collected over the summer months and their health status assessed. Cockles that had surfaced (moribund) and those still buried in the sediment were quantified and screened: sex, gonadal maturity and size class of cockles were also determined. Disseminated neoplasia and trematodes were observed in screened cockles. The most significant finding during the study was that mortalities and surfacing of cockles was related to a greater incidence of disseminated neoplasia. No neoplasia was observed in the smallest and largest size classes. There was a significantly higher prevalence of neoplasia in moribund cockles than in buried cockles, whereas in both groups a similar concentration of trematode metacercariae was observed in the screened tissues. Also, most of the cockles that had surfaced were either in the process of spawning or were spent. Overall a much larger percentage of moribund cockles exhibited both trematode infections plus neoplasia compared with buried cockles. A combination of the presence of neoplasia and trematodes, along with stress related to spawning, may immunocompromise the cockless, causing the animals to surface and become moribund.     

Anatomical observations on the bill of the Oystercatcher (Haematopus ostralegus occidentalis) in relation to feeding behaviour

Oystercatchers have recently increased as inland breeders in Northern Britain. Concurrently, they have been observed feeding in coastal fields in winter. It is suggested that the bill of this species possesses dual characteristics enabling them to feed on shellfish adn also to probe in the soil for terrestrial invertebrates.
The gross internal morphology of the bills of adults and young is described. A bony core contains large nerves running the length of the bill. These break up towards the tip where numerous sensory corpuscles are seen. It is concluded that the possession of a strong bone core together with numerous sense organs at the tip has been of considerable importance in enabling the Oystercatcher to exploit inland situations.     

Observations on the shell morphology of two species of cockle Cerastoderma edule and C. glaucum

Aspects of the shell morphology of the cockles Cerastoderma edule (L.) and C. glaucum (Poiret) collected from the R. Crouch and R. Roach (Essex, England) are considered with reference to interpretation of the environment of sub-fossil assemblages. Discrimination between the two cockle species is best achieved by assessment of qualitative shell characters, quantitative measurements being of rather limited value. Factors influencing shell rib-number differ in the two species of Cerastoderma; within a common environment C. glaucum has fewer ribs than C. edule . Mean rib-number of C. edule is directly related to salinity over the colonized salinity range 20–36.5%₀ whilst in C. glaucum rib-number is lowest in both low (<10%₀) and high (>35%₀) salinity environments, being maximal where salinities between 20–30%₀ occur. Internal shell pigmentation may be absent in C. glaucum from low salinity environments. Magnesium content of whole shells is similar in the two cockle species from a mixed population. In both cockles, however, the prismatic layer contained more magnesium than the nacreous shell layer. The most useful molluscan indicators of brackish water lagoon environments are C. glaucum and Hydrobia ventrosa; these species being absent from areas of only limited wave action. C. edule may be associated with marine or estuarine molluscan indicators.     

First record and description of metacercariae of Curtuteria arguinae n. sp. (Digenea: Echinostomatidae), parasite of cockles Cerastoderma edule (Mollusca: Bivalvia) in Arcachon Bay, France

A new Himasthlinae species, Curtuteria arguinae, is described as metacercariae from the cockle Cerastoderma edule (L.), collected at Banc d'Arguin (southwestern France). These metacercariae encysted preferentially in the mantle and also in the foot of cockles. Encysted and chemically excysted metacercariae were studied by light microscopy and scanning electron microscopy, respectively. Excysted metacercariae were elongated and curved ventrally. They bore a 33-spine circumoral collar. Sensory papillae were arranged around the oral sucker and also symmetrically along the ventral surface body, from the collar to the acetabulum. The dorsal and ventral tegument surfaces were densely packed with similar pointed spines. The posterior end of the body was without any spines. Among the Curtuteria species described previously, only Curtuteria haematopodis Smogorjewskaja and Iskova, 1966 had the same number of circumoral collar spines. A 6-yr field survey showed that the cockle population at Banc d'Arguin was subjected to a summer infection of C. arguinae. Curtuteria arguinae phenology of infection is characterized by interannual variability and seasonality (beginning in July-August and maximum in autumn). The first intermediate and final hosts remain unknown.     

Differential effects of the severe winter of 1995/96 on the intertidal bivalves Mytilus edulis, Cerastoderma edule and Mya arenaria in the Northern Wadden Sea

Intertidal mussel beds were severely damaged by scouring ice floes during the winter of 1995/96. Aerial surveys before and after the winter showed that more clusters of mussel beds vanished in a region with a higher areal share of tidal flats and a lower salinity, suggesting that the amount of ice present determined the magnitude of the disturbance on beds of Mytilus edulis. Nehls and Thiel [(1993) Neth J Sea Res 31:181–187] observed a strikingly similar spatial pattern of disturbances caused by severe storms in the Wadden Sea. Areas on mussel beds mechanically undisturbed by ice showed no reduced abundance and biomass of mussels, indicating that temperature alone was of little importance as a lethal factor. Conversely, Cerastoderma edule was strongly affected by low temperature. On average 80% died during the winter with extinctions up to 100% in the high tidal zone. At the lowest tidal level, surviving cockles were larger than those killed by the frost. A reinvestigation of sampled sites in autumn revealed that substantial further mortality had occurred during spring and summer which may constitute a time-lag effect of the preceding winter. There was no increased mortality in juvenile and adult Mya arenaria during the winter of 1995/96, confirming that this clam is a hard-winter species like Macoma balthica. Received in revised form: 7 May 2001 Electronic Publication